The contradictory experiences of young Japanese—who have low self-esteem, are highly anxious, are pessimistic about their own as well as their country's future, yet still report to be satisfied with their lives—imply that measuring and understanding individual well-being is by no means a straightforward task. This chapter reviews a first step towards reaching a more comprehensive understanding of what matters for the subjective well-being of young Japanese, in order to solve the puzzle of their reported high levels of life satisfaction. Using data from a nationwide postal survey from 2009, it analyzes whether the structure of well-being of young Japanese differs from that of older generations. The chapter includes measures for the material, the interpersonal, as well as the existential dimension of well-being and tests their impact on evaluations of well-being across age with multiple regression models. It discusses results in light of the institutional context in which the different age groups find themselves.